Swine flu outbreak 15 times deadlier: study

A new study has revealed that the swine flu pandemic of 2009 killed an estimated 284,500 people, about 15 times the number confirmed by laboratory tests at the time.

It also shows that more than half the swine flu deaths occurred in Africa and south-east Asia, which account for only 38 per cent of the world's population.

The study, published in the Lancet Infectious Diseases journal, says the global death toll might have been even higher - as many as 579,000 people.

The researchers say the results show that global health authorities must ensure any future vaccine reaches the areas where the death toll is likely to be highest.

The original count was compiled by the World Health Organisation and put the number at 18,500.

Such lab-based identification is the gold standard, but experts acknowledges that it misses more cases than it catches, as some people who contract flu do not have access to health care.

The Lancet researchers started with hard data, such as numbers from health workers going door to door in rural villages and asking about flu-like symptoms and testing swab samples, to estimate the proportion of a country's population infected with 2009 H1N1.

Such data were available from 13 countries - wealthy, such as Denmark, and poor, like Vietnam.

Then the scientists estimated the fraction of patients who died in each country. They started with solid data on death rates from respiratory illnesses in five wealthy nations.

Because someone with pneumonia has a lower chance of dying if treated in a top hospital in Hong Kong than at a rural clinic in Vietnam, the scientists applied a "multiplier" to the raw data from poor countries.

That is, they assumed that more people with flu-caused pneumonia died in developing nations than developed ones.

The results paint a picture of a flu virus that did not treat all victims equally, killing two to three times as many of its victims in Africa as elsewhere.